I often listened to Dr. James Davis (former TAMU extension fisheries specialist) speak to groups on farm pond management. One quote from his repetative presentations has stuck in my mind for a long time.
"More fish have been killed through the misuse of Karmex (aka diuron) than all other pesticides combined." Nuff said.
One should also consider that chemical manufacturers (namely DuPont) would never ignore such a potential high-volume use market (as aquatics) unless there was just cause to do so.